The God Molecule

Book excerpt: Life on Earth has been hacked and genetic coding is understood. Transfer RNA (tRNA) is the core feature in evolution of translation (protein synthesis) systems. The pre-life sequences of the first type I and type II tRNAs are now known with certainty. Pre-life tRNA sequences are a preserved molecular fossil that relate a clear story of the evolution of the genetic code and the origin of life. Because pre-life tRNA sequences were highly ordered (RNA repeats and inverted repeats), tRNA evolution was solved as a puzzle by inspection. The anticodon loop of tRNA is a specialized feature that was likely required to evolve living systems with a 3-nucleotide genetic code. To generate life on Earth or another moon or planet requires tRNA or another genetic adapter that is just as good. The genetic code evolved around the tRNA anticodon and its reading on the primitive ribosome. Analysis of tRNA, therefore, provides clear insights into evolution of the genetic code, ribosomes and the origin of life.